Draining Disease

You summon a malicious dark entity in the shadow of a target. At the beginning of the targets turn, they take 1d4 necrotic damage and 1d4 poison damage. When the target is reduced to zero hit points this effect spreads to all creatures within 10 feet. This spell can be cancelled at will by the caster, or with a cast of any effect that would remove poison, disease or dispel magic.

At higher levels: 

When cast with a spell slot of level 5 or higher, the damage increases to 1d6 poison and 1d6 necrotic instead.